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Publications
Publications (41)
The European eel's singular spawning migration from European waters towards the Sargasso Sea remains elusive, including the early phase of migration at sea. During spawning migration, the movement of freshwater resident eels from river to sea has been thought to be irreversible. We report the first recorded incidents of eels returning to the river...
The European eel's singular spawning migration from European waters towards the Sargasso Sea remains elusive, including the early phase of migration at sea. During spawning migration, the movement of freshwater resident eels from river to sea has been thought to be irreversible. We report the first recorded incidents of eels returning to the river...
Relationships between biomass and ecological factors including trophic interactions were examined to understand the dynamics of six fish species in Lake Võrtsjärv, a large shallow eutrophic lake located in Estonia (north-eastern Europe). The database contained initially 31 predictive variables that were monitored in situ for nearly forty years. The...
We numerically explored the effects of long-term water level changes on biotic biomass and spatial distribution of fish in a large shallow lake. We calibrated Ecospace model (Ecopath with Ecosim modelling suite) with data from various functional groups (ranging from phytoplankton to piscivorous fish), and considered 14 different habitats. Two scena...
We modeled energy transfer and trophic position of fish, plankton, and macroinvertebrates and the relative importance of top-down versus bottom-up processes in Lake Võrtsjärv, a large shallow eutrophic lake in Estonia (northeastern Europe). We employed input values based on 37 years of biomass and fishing activity monitoring for calibrating the Eco...
p>Through cascading effects within lake food webs, commercial and recreational fisheries may indirectly affect the abundances of organisms at lower trophic levels, such as phytoplankton, even if they are not directly consumed. So far, interactive effects of fisheries, changing trophic state and climate upon lake ecosystems have been largely overloo...
In the previous report (D4.1, September 2016) we have developed predictive linkages between indicators of environmental quality and ecosystem services, and different types of pressures, single or multiple, across river basins from all over Europe, in a latitudinal and a west-east gradient, and having very different conditions of climate and land us...
To investigate the difference in growth rates of eels in the studied water bodies (Võrtsjärv, Ülemiste, Saadjärv, Vagula, Kaiavere and Kuremaa lakes, all in Estonia), 828 individual eel otoliths from the years 1999–2004 and 2008–2012 were examined for age determination. Anguilla anguilla captured in Lake Võrtsjärv mostly by professional fyke nets (...
Efficient zooplankton grazing is a prerequisite for establishing a cascading food web control over phytoplankton in a lake. We studied if the top-down impact of fish could reach phytoplankton in a lake where the grazing pressure of small-sized zooplankton on filamentous phytoplankton is considered weak. We analysed >30 years of data on plankton, fi...
This study is the first attempt at the European scale to make an inventory of ecosystem services (ESS) of a large lake. We analysed a set of ESS indicators against the annual mean values of environmental parameters for 2006–2013. According to principal component analysis, the trophic state- and hydrology-related factors explained about 70% of the e...
Part 1:
This deliverable consists two manuscripts (MS) of lake time-series analysis in north-temperate
region of Europe.
1st MS: ‘Is fish able to regulate filamentous blue-green dominated phytoplankton?’
submitted to ‘Hydrobiologia’, analyzes >40-year data on biota, fish catches, hydrochemistry,
hydrology, and meteorological parameters in Lake Võrt...
Part 1:
This deliverable consists two manuscripts (MS) of lake time-series analysis in north-temperate
region of Europe.
1st MS ‘Is fish able to regulate filamentous blue-green dominated phytoplankton?’
submitted to ‘Hydrobiologia’, analyzes >40-year data on biota, fish catches, hydrochemistry,
hydrology, and meteorological parameters in Lake Võrts...
European eel stocks are in a decline all over Europe. In Estonia, we analysed three different dataseries (commercial landings
1969–2014, scientific eel monitoring 1998–2014, and recreational catches 2005–2012). In the commercial fishery, the biggest
drop in landings occurred in the 1980s, with a small recovery in the end of the 1990s. We also inter...
European eel (Anguilla anguilla) has one of the most intriguing life cycles of all fishes. Its larvae drift in the early stages of the species life as well as the spawning run in the maturity stretches to thousands of kilometres, from Europe to Sargasso sea. In between the eel may inhabit both brackish- and freshwater systems. Due to different natu...
The construction of the Ivangorod HPS in the early 1950s blocked totally the natural upstream migration of young eel from the Baltic Sea to the Narva River basin. Due to the rather permanent introduction of glass eels or farmed eels into L. Võrtsjärv (since 1956) and four small lakes (since 2003), it has become one of the most important commercial...
European eel (Anguilla anguilla) stock has been in decline for decades and the fixtures for eel catches in the Baltic Sea show a steady diminishing rate . European Union has stated that serious measures have to be implemented concerning the decline of the eel stock (Council Regulation No 1100/2007). Furthermore this regulation requires all member s...
The influence of functional group specific production and respiration patterns on a lake's metabolic balance remains poorly investigated to date compared to whole-system estimates of metabolism. We employed a summed component ecosystem approach for assessing lake-wide and functional group-specific metabolism (gross primary production (GPP) and resp...
Whole-lake metabolism has been receiving growing attention recently as lakes are supposed to have large effects on regional carbon balance. However, the contribution of lake functional groups to whole-lake metabolism remains poorly known. In this study we assessed respiration and primary production of different trophic levels of Võrtsjärv, a large,...
Eel fishery in Estonian inland waters depends entirely on the stocking of glass eels or pre-grown (farmed) eels. Via importation of live eels of 20–30 cm length the non-indigenous swimbladder nematode Anguillicoloides crassus was probably introduced via Germany into Lake Võrtsjärv in 1988, and has since spread to many inland waters of Estonia. In 1...
Lake Ülemiste, the drinking water reservoir of Estonia’s capital city Tallinn, was biomanipulated by manual removal of cyprinids
in 2004–2006 and its impact on water quality in the vegetation period was studied. A total biomass of 156tonnes corresponding
to 160kgha−1 of fish, predominantly cyprinids, were removed. A decline in the unit catches of f...
Small Estonian inland waters are characterized as hard/soft, dark/bright and shallow/ stratified. Our surveys by multimesh Nordic gill-netting in 1996-2009 showed the highest values of species richness, abundance and catch in moderately hard waters inhabited also by species such as Sander lucioperca, Cobitis taenia, Gobio gobio, Leuciscus idus, Asp...
According to the European Council Regulation of establishing measures for recovery of the stock of eel, the principal element is to achieve the objective of a 40% escapement of adult silver eel from each river basin. The construction of the hydroelectric power station on the Narva River in the early 1950s blocked the natural path of eel to the wate...
The possibility of utilizing biomanipulation to improve the water quality of Tallinn's drinking water reservoir (Lake Ülemiste) was analysed on the basis of water quality data, test fishing by different methods, and earlier studies on aquatic plants, light climate and sediments. Eutrophic, polymictic Lake Ülemiste is characterized by a prevalence o...
The diel migration and spatial distribution of fish were explored using six sequential 4-h sample gillnettings in the pelagic
and littoral zones of Lake Verevi (Estonia, 12.6 ha, max. depth 11 m, hard-water, deoxygenated hypolimnion) in August 2001
and July 2002. Considering abundance, two-thirds of the total fish moved to the littoral zone. The bi...
Stratified lakes often receive more attention from limnologists although most of the world's lakes are indeed shallow. This study describes ecological processes in three shallow lakes, one dominated by macrophytes, one by phytoplankton, and one with both of them. Investigations focused on abiotic (water chemistry) as well as biotic factors such as...
The diel migration and spatial distribution of fish were explored using six sequential 4-h sample gillnettings in the pelagic and littoral zones of Lake Verevi (Estonia, 12.6 ha, max. depth 11 m, hard-water, deoxygenated hypolimnion) in August 2001 and July 2002. Considering abundance, two-thirds of the total fish moved to the littoral zone. The bi...
The present study describes generally the ecosystem of Lake Verevi while more detailed approaches are presented in the same issue. The main task of the article is to estimate long-term changes and find the best method for the restoration of good ecological status. Lake Verevi (surface 12.6ha, mean depth 3.6m, maximum depth 11m, drainage area 1.1km2...
Lake Võrtsjärv is a large (area 270 km2), shallow (maximum depth 6.0 m) and turbid eutrophic lake in which eel Anguilla anguilla (L.), pikeperch Sander lucioperca (L.), northern pike Esox lucius L. and bream Abramis brama (L.) are the main commercial fishes, while perch Perca fluviatilis L. and burbot Lota lota (L.) are of secondary economic import...
The present study describes generally the ecosystem of Lake Verevi while more detailed approaches are presented in the same issue. The main task of the article is to estimate long-term changes and find the best method for the restoration of good ecological status. Lake Verevi (surface 12.6 ha, mean depth 3.6 m, maximum depth 11 m, drainage area 1.1...
1.The European Water Framework Directive requires the determination of ecological status in European fresh and saline waters. This is to be through the establishment of a typology of surface water bodies, the determination of reference (high status) conditions in each element (ecotype) of the typology and of lower grades of status (good, moderate,...
1. The European Water Framework Directive requires the determination of ecological status in European fresh and saline waters. This is to be through the establishment of a typology of surface water bodies, the determination of reference (high status) conditions in each element (ecotype) of the typology and of lower grades of status (good, moderate,...
Lake Võrtsjärv is a large (area 270 km2) shallow (maximum depth 6.0 m) eutrophic lake. Eel, pikepereh, bream, and pike are the main eommercial fishes in the lake, while pereh, roach, ruffe, and burbot are of seeondary eeonomie importanee. High water level in the lake in spring expands the spawning areas of pike and has astrong positive influenee on...
In the18th and 19th centuries the first data on fisheries, hydrology, and aquatic vegetation in Lake Võrtsjärv were published by Baltic German naturalists. The comprehensive investigation by the Lake Commission of the Estonian Naturalists' Society in 1911–13 led by M. von zur Mühlen is a milestone in the scientific level. During more than 30 years...
Data on the biomass and productivity of phytoplankton, bacteria, metazooplankton, macrozoobenthos and fishes in eutrophic Lake Võrtsjärv (270 km2, mean depth 2.8 m) were used to construct the carbon balance of the lake. The average annual biomass (g C m-2) and production (g C m-2 y-1) of different links of the food web were the following: phytoplan...
Virtual Populations Analysis (VPA) of the data on catch number by age and year, is used to estimate fishing mortality, abundance and biomass of the fishable stock of pikeperch in Lake Võrtsjärv (270 km2, mean depth 2.8 m), Estonia. The catch rate of the fishery is rather low, finishing mortality (F) of the dominant age group (4-10 years) was 0.21-0...
Projects
Project (1)
Lakes form 4% and their catchments >50% of land cover in Estonia making it the 4th richest country by lakes in Europe. Lakes receive increasing natural and anthropogenic loads of substances from their catchments. To a certain limit, healthy lake ecosystems bury these substances in their sediments or convert them into bio-production keeping the water clean, and rather bind than emit greenhouse gases. It is important to prevent, but if present, recognize and cure disorders in lake ecosystem functioning. Over its nearly 60-year existence, Centre for Limnology of EMU has become a unique centre of competence in Estonia collecting data and know-how and educating people for water protection, research and management. The basic task of the proposed project is to maintain and develop in Estonia the internationally acknowledged competence on carbon cycling and lake food webs that would sustain knowledge based water policy and compliance with international obligations in global change conditions.
